IBC is the most lethal form of primary breast cancer and disproportionately targets younger women. IBC accounts for <5% of all breast cancer cases in the United States, but its incidence is significantly higher among African-American women (10.1%). In Egypt, the incidence of IBC is reported to be from 5- 10% of all breast cancer cases and is on the rise. Extensive dermal lymphatic invasion and tumor emboli therein result in lymphatic obstruction that underlies the inflammatory nature of the disease. We have shown that macrophages infiltrate the IBC microenvironment, surround IBC emboli and are present in axillary blood of IBC patients. Our working hypothesis in this proposal is that IBC-associated macrophages play a crucial role in the formation of tumor emboli and dissemination of the cancer cells in the lymphatics, two of the phenotypic hallmarks of IBC. The Specific Aims of this FIRCA proposal are to: 1) Establish 3D cultures of IBC cells and a) assess invasive phenotype; b) determine expression/localization of putative IBC marker proteins; c) quantify expression of cytokines, chemokines and growth factors in conditioned media; and d) expression/secretion/activity of cysteine cathepsins; 2) Characterize monocyte/macrophage phenotype and content in tumor emboli, tumors, positive lymph nodes, axillary tributary blood and peripheral blood from IBC and non-IBC patients; 3) Isolate monocytes from IBC axillary tributary blood and peripheral blood and a) quantify expression of secreted cytokines, chemokines and growth factors, and b) expression/secretion/activity of cysteine cathepsins; 4) Immunostain paraffin blocks of IBC specimens for cell surface receptors of selected cytokines, chemokines and growth factors; and, 5) Establish 3D cocultures of IBC cells and monocytes isolated from IBC axillary tributary blood and peripheral blood and a) assess invasive phenotype; b) determine expression/localization of putative IBC marker proteins; c) quantify expression of cytokines, chemokines and growth factors in conditioned media; and d) expression/secretion/activity of cysteine cathepsins; and, e) immunostain cocultures for cell surface receptors identified in IBC specimens. Future directions will use the information obtained in Aims 1-5 to select cysteine cathepsins, cytokines, chemokines and growth factors that might be targeted to reduce the invasive phenotype of IBC. The aggressive manifestation of IBC in Egypt means that there is a pressing need to develop research programs that can be of immediate assistance to patients suffering from breast cancer. We anticipate that our results will contribute to the characterization of the pathobiological underpinnings of IBC, a prerequisite for prioritizing novel targets for therapeutic intervention. This research will be done primarily in Egypt at Cairo University in collaboration with Mona Mostafa Mohamed, as an extension of NIH Grant No. R01CA131990, 8-01-2008 to 5-31-2013.